> I remember way back (when XHTML was still on the table) that innerHTML was effectively deprecated
I had heard that document.write is discouraged but not innerHTML. In fact, browsers have doubled down, by adding insertAdjacentHTML (originally only in Internet Explorer).
> Instead, you were supposed to use the DOM APIs
I tried that in an app. It turned out that IE 6 was faster with innerHTML, like literally 1,000 times faster. This was surprising because I assumed the DOM APIs were closer to the metal. Not so, at least with Internet Explorer. (With Chrome, the DOM APIs and innerHTML were about the same speed).
> standard compliance and future support
It will be supported forever, because browsers refuse to break the web. You can see them saying so when they discuss syntax for new features.
Mozilla's documentation tells you when a feature is deprecated (again, usually for a feature that was experimental and never widespread). It carries no such notice on its page for innerHTML. It does, however, carry a warning: "Warning: If your project is one that will undergo any form of security review, using innerHTML most likely will result in your code being rejected." --- https://developer.mozilla.org/en-US/docs/Web/API/Element/inn...
To me, innerHTML is sometimes useful and no more dangerous than server-side rendering. Rather than deprecating it, I wonder why browser vendors have not added a native escapeHTML function (or even better, a very short syntax) to make innerHTML safer.